The response of nitrogen removal and related bacteria within constructed wetlands after long-term treating wastewater containing environmental concentrations of silver nanoparticles

The wide application of consumer products containing silver nanopartides (AgNPs) inevitably results in their release into sewer systems and wastewater treatment plants, where they would encounter (and cause potential negative impacts) constructed wetlands (CWs), a complex biological system containing plants, substrate and microorganisms. Herein, the long-term effects of environmental AgNPs concentrations on nitrogen removal, key enzymatic activities and nitrogen-related microbes in constructed wetlands (CWs) were investigated. The shortterm exposure (40 d) to AgNPs significantly inhibited TN and NH4+-N removal, and the inhibition degree had a positive relationship with AgNPs levels. After about 450 d exposure, 200 mu g/L AgNPs could slightly increase average TN removal efficiency, while presence of 50 mu g/L AgNPs showed no difference, compared to control. TheNH(4)(+)-N removal in all CWs had no difference. The present study indicated that short-term AgNPs loading evidently reduced nitrogen removal, whereas long-term exposure to AgNPs showed no adverse impacts on NH4+-N removal and slightly stimulated TN removal, which was related to the increase of corresponding enzymatic activities. After exposing AgNPs for 450 d, the abundance of relative functional genes and the composition of key community structure were determined by qPCR and high-throughput sequencing, respectively. The results showed that the abundance of amoA and nxrA dramatically higher than control, whereas the abundance of nirK, nirS, nosZ and anammox 16S rRNA was slightly higher than control, but had no statistical difference, which accorded with the TN removal performance. The microbial community analysis showed that different AgNPs concentrations could affect the microbial diversity and structure. The changes of the relative abundance of nitrogen-related genera were associated with the impacts of AgNPs on the nitrogen removal performance. Overall, the AgNPs loading had impacts on the key enzymatic activities, the abundance of nitrogen-related genes and microbial community, thus finally affected the treatment performance of CWs. (C) 2019 Elsevier B.V. All rights reserved.